1. Field of the Invention
The present invention relates to a system for loading and unloading of cold media, for example LNG or LPG, to or from a vessel, especially offshore.
2. Description of the Prior Art
Today the loading and unloading of liquid natural gas or other cooled down hydrocarbons take place offshore only as an exception. Wishes to do this offshore are, however, increasingly natural. Floating factories for liquid natural gas, so called LNG, are being planned out on the open ocean. Therefore the need for effective loading system is present.
Such a system is described in Norwegian patent application 1998 1332 which contains descriptions of such loading systems. The loading system itself consists of pipes connected with spherical ball joints. In addition what is described, the solution will be equipped with some type of insulation. This is because the liquid LNG has a temperature of about xe2x88x92162xc2x0 C. at atmospheric pressure.
This insulation has the task of minimize the loss of energy and the costs in this connection. Further it is important to avoid cold surfaces where sea spray or moisture may form heavy layers of ice. Further task is to avoid that ice is formed of ball joints smooth spherical surfaces. Such ice will be able to hinder the movement and damage the gasket and thereby make the system unusable.
Finally, the insulation should delay boiling if the loading is stopped and pieces of pipe get under water.
Most types of insulation used on ship and in the offshore industries is based on the fact that they contain a gas, usually air, which hinder both heat conduction and heat radiation. But even if the heat radiation through the insulation is small, will heat conduction not be less than the heat conductivity of air.
It is estimated that, if this insulation shall meet the tasks as given above, there is a need for a 140 mm thick layer of insulation. This is problematic, especially for the ball joint, where the insulation must be mounted inside.
The porous material must also be protected against a considerable mechanical wear and hits during various operations. This will further mean problems with being able to dismount and inspect insulation and piping as demanded by classification companies and others.
The present invention will avoid most of the above disadvantages with known solutions, while it achieves other important advantages.
Accordingly, the present invention is a ball joint coupling apparatus for loading and unloading of cold liquid gas media to or from a vessel through insulated pipes (1) connected with the ball joint coupling apparatus. The invention is characterized in that the ball joint coupling apparatus has an inside part (4) which surrounds an inside pipe (3). The inside pipe (3) is sealed against the inside part (4) substantially over the extent of the inside part (4), thereby forming an inside annulus (6) which is evacuated.
The invention is also characterized in that the ball joint coupling apparatus has an outside part (10) which is surrounded by an outside annulus (9) which is also evacuated.